Amplifier Power Plot Characteristics

I am simulating a three-stage amplifier and inputting parameters into the nonlinearity settings for one of the amplifiers. However, after plotting the results, the OP1dB shown on the plot does not match the value from the datasheet, even though Psat and OIP3 are plotted correctly. Why is this happening, and how can I get the correct OP1dB value to appear? I'm using an s2p file for this amplifier.

Also, kindly explain the differences of the plots when using even and odd order or odd order only.

Thanks!